The present invention relates to a traffic shaping circuit, a terminal device and a network node. It particularly relates to a traffic shaping circuit in a fixed- or variable-length packet transmission terminal or a network node (such as a router), the transmission terminal and the network node.
There is increasing importance of a quality of service function (hereinafter referred to as QoS function) in packet communication implemented using an asynchronous transfer mode (ATM) switch, a router, etc. As typical examples of the QoS function, there are priority control (low latency period transfer), discard control (low discard rate transfer), bandwidth control (maximum or minimum bandwidth ensuring transfer), etc. Among these, the bandwidth control is a function for dividing a physical line bandwidth into logical bandwidths and transmitting/receiving packets in the divided logical bandwidths. For example, the bandwidth control is the QoS required for bandwidth provision service for providing a constant bandwidth based on a contract between each user and a network. For example, the bandwidth control is effective in the case where completion of the service needs to be guaranteed within a target time at the time of distribution of contents or backup of a storage device.
In a packet transmitting line of an ATM switch, a router etc., a chunk of information (hereinafter referred to as packets) called cells or packets are outputted to a port in accordance with predetermined rules (shaping model) provided in a shaping circuit so that the aforementioned QoS is implemented. The shaping circuit classifies a variety of packets to be outputted to one and the same port in the device in accordance with kinds of flow, accumulates the variety of packets in queuing buffers once, and outputs the variety of packets from the queuing buffers in accordance with priorities and bandwidth target values. As examples of the shaping model, there are a priority control model, a bandwidth control model, and a multistage hierarchical shaping model.
First, the priority control model is a model in which packets of a high priority queue among queues to be outputted to one and the same line are outputted with priority over packets of the other queues so that the staying time of the packets of the high priority queue in the device is shortened and low latency transfer is therefore implemented. Maintaining service of quality of high-priority packets by this priority control model is suitable, for example, for low latency transfer of VOICE, video etc. and low discard rate transfer of mission critical data. It was however difficult to offer fair bandwidth service based on contracted bandwidths among contract parties (users) (Background Art 1).
Next, the bandwidth control model is a model carried out as follows by way of example. That is, logical bandwidth values are set respectively for packet queues to be outputted to one and the same line so that packets are outputted from the queues which are changed from one to another based on the bandwidth values. In this manner, transfer is implemented while the logical bandwidth values of the respective queues are complied with. A next packet transmission appointed time is calculated, for example, by a leaky bucket model. The leaky bucket model has been described, for example, in “The ATM Forum TM4.0 Normative Annex C: Traffic Contract Related Algorithms and Procedures, P. 62, 63” (Non-Patent Document 1). Although it is possible to use the bandwidth control model to offer bandwidth provision service, i.e. SLA (Service Level Agreement) management service for sharing one and the same line bandwidth among contract parties (users) each consequently using a contracted bandwidth (logical bandwidth), it was difficult to selectively provide priority control over packets which needs to be transferred with low latency in the contracted bandwidth (Background Art 2).
The hierarchical shaping model can be also regarded as a model of combining rules of the aforementioned Background Art 1, Background Art 2, etc. For example, Background Art 3 has been described in Patent Document 1. In Embodiment 4 of Patent Document 1, for example, contracted bandwidths of users with a network are allocated respectively to the users for variable-length packets to be outputted from the users to one and the same port. In a priority control circuit 15210, packets from one and the same user are classified into queues corresponding to transfer priorities judged based on information of transfer destinations, priorities, etc. so that priority control over the queues in the allocated contracted bandwidth is performed. In this manner, while one and the same line is divided into contracted bandwidths used by users, priority control service in the contracted bandwidths can be offered simultaneously. Low latency period transfer is offered by transferring low latency packets of a user with priority over the other priority packets in the contracted bandwidth of one and the same line. It is possible to provide a traffic shaping device for a packet transmission terminal or a packet switch, which can effectively use the line bandwidth and the contracted bandwidth of each user.    [Patent Document 1] Japanese Patent Laid-Open No. 2000-31974    [Non-Patent Document 1] “The ATM Forum TM4.0 Normative Annex C: Traffic Contract Related Algorithms and Procedures”, P. 62, 63,